1. Technical Field
The present invention relates to a switching device for switching on and off by the operation of a swingable operation knob, and more particularly to a waterproof-type switching device which is capable of preventing water from entering into its case.
2. Description of the Related Art
FIG. 10 illustrates an external appearance of a switching device 100 as an example used in a vehicle window opening and closing system (power window system). The switching device 100 includes a case 1 which is constituted by an upper case 1a and a lower case 1b. While a part of the lower case 1b is shown in FIG. 10, the lower case 1b actually engages with the lower portion of the upper case 1a as illustrated in the cross-sectional view of FIG. 13. A plurality of projections 1c are formed on the lower case 1b, and a plurality of holes 1d are formed on the upper case 1a, as illustrated in FIG. 10. For assembling the case 1, the projections 1c are brought into engagement with the holes 1d so as to fix the upper case 1a and the lower case 1b to each other.
Components such as a switch and a circuit board which will be described later are accommodated within the case 1. Attachments 2 for attaching a cover which will be described later are formed on the upper region of the case 1. A connector 3 is connected with a connection cable used for connection with a controller (not shown). An operation knob 4 of a door lock switch is operated for locking the respective doors of the vehicle such that they cannot be opened, or for releasing the lock. An operation knob 5 of a window lock switch is operated for locking the respective windows of the vehicle such that they cannot be opened or closed, or for releasing the lock. Four operation knobs 6 of a window opening and closing switch are operated for opening and closing the respective windows of the vehicle. The operation knob 4 and the operation knobs 6 are seesaw-motion type knobs capable of swinging like a seesaw, and the operation knob 5 is a knob formed by a lock-type push button. The operation knob 6 includes operation sections 6a, cap sections 6b formed integrally with the operation sections 6a, and holes 6c formed on the side walls of the cap sections 6b. While one hole 6c on each operation knob 6 is shown in FIG. 10, the same hole as the hole 6c is formed on the side wall opposite to the side wall where the hole 6c is provided.
FIG. 11 illustrates an external appearance of the case 1 shown in FIG. 10 from which the four operation knobs 6 are removed. In the figure, cylindrical sections 7 provided on an upper surface 1e of the case 1, shaft members 7a formed integrally with the outer walls of the respective cylindrical sections 7, and upper openings 7b of the cylindrical sections 7 which open to above are shown. While one shaft member 7a on each cylindrical section 7 is illustrated in FIG. 11, the same shaft member as the shaft member 7a is formed integrally with the outer wall opposite to the outer wall where the shaft member 7a is provided. By attaching the cap sections 6b of the operation knobs 6 to the cylindrical sections 7 from above such that the cap sections 6b can cover the upper openings 7b, and engaging the shaft members 7a of the cylindrical sections 7 with the holes 6c of the operation knobs 6, the case 1 is brought to the condition shown in FIG. 10 and the operation knobs 6 are supported by the cylindrical sections 7 such that the operation knobs 6 can swing around the shaft members 7a. 
FIG. 12 illustrates an external appearance of the switching device 100 shown in FIG. 10 to which a cover 8 is attached. The cover 8 covers the switching device 100 in the area other than the operation knobs 4 through 6 when the switching device 100 is attached to an arm rest (not shown) provided on the door of the driver's seat of the vehicle. The cover 8 has bosses 9, and the cover 8 is attached to the switching device 100 by fitting screws (not shown) inserted from the back of attachments 2 of the case 1 to screw holes (not shown) formed on the bosses 9. Four openings 8a through which the fingers are inserted to operate the operation sections 6a of the respective operation knobs 6 are formed on the cover 8, and the operation sections 6a are exposed through the openings 8a. Openings 8c and 8d through which the operation knob 4 and the operation knob 5 are exposed, respectively, are also formed. The opening areas of the openings 8c and 8d are small since the operation knobs 4 and 5 are only pushed from above for operation. However, the opening areas of the openings 8a are large since the operation knobs 6 need to be lowered and raised with the fingers being putted on the operation section 6a. 
FIG. 13 is a cross-sectional view of the switching device 100 to which the cover 8 is attached. As apparent from the figure, the cylindrical sections 7 are cylindrical hollow components which open to above and below and communicate with the inside of the case 1. A circuit board 10 is equipped within the case 1, and switches 11 are mounted on the circuit board 10. The switches 11 are switches for opening and closing the windows, and are constituted by known slide switches. Actuators 11a for the switches 11 are provided. Operation bars 12 connected with the operation knobs 6 penetrate through lower openings 7c of the cylindrical sections 7 and extend to the inside of the case 1. Concaves 12a are formed at the lower ends of the operation bars 12. Through the engagement between the concaves 12a and the actuators 11a of the switches 11, the motions of the operation knobs 6 are transmitted through the operation bars 12 to the switches 11 such that contacts provided inside the switches 11 can be switched on and off in accordance with the operation positions of the operation knobs 6.
Switching devices having a structure similar to that of the above switching device 100 are disclosed in JP-A-8-180755 and JP-A-5-314864. JP-A-11-86662 shows a similar switching device which is waterproofed by surrounding soldered portions of electronic component terminals on a circuit board with side walls formed by rubber contact members without requiring coatings.
In the known switching device 100 shown in FIG. 12, however, there is a possibility that raindrops coming through the windows left opened or beverages accidentally spilled inside the vehicle enter through the openings 8a into concaves 8b (see FIG. 13), since the opening areas of the openings 8a of the cover 8 are large. Since the volumes of the concaves 8b are considerably large such that the operation by the fingers can be carried out without trouble, the entering water passes through clearances 13 between the cover 8 and the operation knobs 6 and clearances 14 between the operation knobs 6 and the cylindrical sections 7 as shown by an arrow in FIG. 13 when the amount of the water flown into the concaves 8b is large. The water then enters from the upper openings 7b of the cylindrical sections 7 into the cylindrical sections 7, passes through the lower openings 7c of the cylindrical sections 7, and reaches the inside of the case 1. No description about waterproofing of water entering through the lower portions of the operation knobs 6 is made in either JP-A-8-180755 or JP-A-5-314864. Also, while JP-A-11-86662 discloses the waterproofing technique for preventing short-circuit, entering of water through the lower portions of the operation knobs into the inside of the case cannot be prevented in such a switching device which does not employ rubber contacts according to the technique shown in this reference.